1. Field of the Invention
The present invention relates to a video projector. In particular, the invention relates to a video projector using a reflection type optical modulation element.
2. Description of the Prior Art
Video projectors for projecting an image in accordance with a received video signal are known.
Among those video projectors is one using a transmission type optical modulation element such as an LCD (Liquid Crystal Display) panel or the like and one using a reflection type optical modulation element such as a DMD (Digital Micromirror Device: a trademark of Texas Instruments, Incorporated) or the like.
Conventional video projectors using a reflection type optical modulation element will be described here with reference to the drawings.
FIG. 6 is a side view showing the structure of a video projector as a first conventional example. FIG. 7 is a sectional plan view taken along a line VIxe2x80x94VI in FIG. 6.
In the video projector shown in FIGS. 6 and 7, light emitted from an optical source 101 is reflected by a reflecting mirror 102 and thereby condensed onto a rod-shaped optical integrator 103. The light is reflected plural times in the rod-shaped optical integrator 103 and then output therefrom in a state that its illumination intensity distribution is uniformized.
The light exiting from the rod-shaped optical integrator 103 sequentially passes through relay lenses 104a-104c reflected by a reflecting mirror 105, passes through a relay lens 104d, and then reflected by the bonding surface of wedge-shaped prisms 106a and 106b that configure a reflecting prism 106.
The light reflected by the reflecting prism 106 is separated by color prisms 107R, 107G, and 107B into red light, green light, and blue light, respectively, which enter DMDs (Digital Micromirror Device: atrademark of Texas Instruments, Incorporated) 109R, 109G, and 109B, respectively.
The DMDs 109R, 109G, and 109B are supplied with video signals corresponding to red, green, and blue components, respectively. The reflectance values of the incident light beams are controlled on a pixel-by-pixel basis in accordance with those video signals.
Light beams reflected by the DMDs 109R, 109G, and 109B enter color prisms 107R, 107G, and 107B, respectively, whereby the red light, green light, and the blue light are combined into full-colored image light. The full-colored image light passes through the reflecting prism 106 straightly and is then enlarged by a projecting lens 110.
The light enlarged by the projecting lens 110 is projected onto a screen 111 as a projected image.
Japanese Patent Laid-Open No. Hei 9-96867 (Laid-Open in Japan on Apr. 8, 1997) discloses a video projector. The technique disclosed in this publication will be described below as a second conventional example.
FIG. 8 is a side view showing the structure of a video projector as a second conventional example. FIG. 9 is a plan view of the video projector of FIG. 8.
The video projector shown in FIGS. 8 and 9 has an optical radiating system 212, a tri-colored optical separating system 214, DMDs 216R, 216G, and 216B, and a projecting lens system 218.
The optical radiating system 212 is composed of an optical source 220, a condenser lens 222, a mirror 224, and a prism 226. White-colored light emitted from the optical source 220 is condensed by the condenser lens 222, reflected by the mirror 224, again reflected by the prism 226, and then enters the tri-colored optical separating system 214.
The white-colored light entering the tri-colored optical separating system 214 is separated by prisms 228R, 228G, and 228B into red light, green light, and blue light, respectively, which enter the DMDs 216R, 216G, and 216B that are disposed behind the respective prisms 228R, 228G, and 228B.
Light beams reflected by the respective DMDs 216R, 216G, and 216B are combined by the prisms 228R, 228G, and 228B and then projected onto a front screen (not shown) by lenses 234 and 236 of the projecting lens system 218.
However, the video projectors as the two conventional examples have the following problems.
In the first conventional example, first, since it is difficult to make the diameter of a light beam sufficiently small at the pupil position 110p of the projecting lens 110, it is impossible to cause all of light beams emitted from the optical source 101 to pass to the pupil position 110p of the projecting lens 110 without undue loss of light, resulting in a problem that a high-brightness, high-contrast projected image cannot be obtained.
Second, if to solve the first problem it is attempted to make the diameter of a light beam sufficiently small at the pupil position 110p of the projecting lens 110 by using the relay lenses 104a-104d, many relay lenses 104a-104d need to be combined in a complex manner, resulting in a problem that the transmittance of the relay lenses 104a-104d decreases and hence a high-brightness, high-contrast projected image cannot be obtained. Moreover, this complicated structure of the relay lenses 104a-104d increases their volumes; thus the video projector cannot be miniaturized.
The above problems also occur in the video projector as the second conventional example in completely the same manners.
An object of the present invention is therefore to provide a video projector using a reflection type optical modulation element whose lens system is simple in configuration and which can produce a high-brightness, high-contrast projected image.
According to a first aspect of the invention, there is provided a video projector having an optical source for radiatinglight; a reflecting mirror for reflecting the light radiated by the optical source as a reflected light beam goes along a particular optical axis; a converting optical system for converting a profile of the reflected light beam from the reflecting mirror; a plurality of color prisms for wavelength-separating the converted-light from the converting optical system into a plurality of colored light beams; a plurality of reflection type optical modulation elements for selectively reflecting each of the colored light beams from the color prisms on a pixelxe2x80x94pixel basis in accordance with each of received video signals, respectively; a projecting lens for projecting light obtained through wavelength-combining, by the color prisms, of light beams reflected by each of the reflection type optical modulation elements; and a plurality of condenser lenses disposed between the color prisms and the reflection type optical modulation elements, respectively.
According to a second aspect of the invention, in the video projector according to the first aspect, further having a relay lens disposed between the converting optical system and the color prisms.
In the video projector according to the first and second aspects of the invention, the condenser lenses corresponding to the respective colors are disposed immediately before the reflection type optical modulation elements corresponding to the respective colors. Therefore, the diameter of a light beam at the pupil position of the projecting lens can sufficiently be decreased, and hence all of a light beam emitted from the optical source can be used effectively without undue loss of light. Further, since the number of lenses configuring the lens system disposed between the optical source and the reflection type optical modulation elements can be reduced; the light transmittance can be kept high. As a result, the brightness and the contrast of a projected image on the screen can be increased.
Further, since the diameters of the condenser lenses can greatly be decreased, the video projector can be miniaturized.
According to a third aspect of the invention, in the video projector according to the second aspect, wherein the converting optical system has a rod-shaped optical integrator.
According to a fourth aspect of the invention, in the video projector according to the third aspect, wherein the reflecting mirror, the rod-shaped optical integrator, the relay lens, the condenser lenses, the reflection type optical modulation elements, and the projecting lens are disposed so as to satisfy: a relationship (d1/d2)=(f1/f2) where d1 denotes a distance between an incident surface and an outgoing surface of the rod-shaped optical integrator, d2 denotes a distance between the relay lens and each of the reflection type optical modulation elements, f1 denotes a focal length of the reflecting mirror, and f2 denotes a focal length of the relay lens; and a relationship (1/f3)=(1/d3)+(1/d4) where d3 denotes a distance between the incident surface of the rod-shaped optical integrator and each of the condenser lenses, d4 denotes a distance between each of the condenser lenses and a pupil position of the projecting lens, and f3 denotes a focal length of each of the condenser lenses.
In the video projectors according to the third and fourth aspects of the invention in which the rod-shaped optical integrator is used as the converting optical system, (1) an image on the outgoing surface of the rod-shaped optical integrator is converged on the reflection type optical modulation elements without undue loss of light, and (2) an image on the incident surface of the rod-shaped optical integrator is converted into a small cross-section at the pupil position of the projecting lens. Therefore, all of light beams emitted from the optical source can be used effectively without undue loss of light. Further, since the number of lenses configuring the lens system disposed between the optical source and the reflection type optical modulation elements can be reduced; the light transmittance can be kept high. As a result, the brightness and the contrast of a projected image on the screen can be increased.
Further, since the diameters of the condenser lenses can greatly be decreased, the video projector can be miniaturized.
According to a fifth aspect of the invention, in the video projector according to the second aspect, wherein the converting optical system has first and second fly-eyed lenses.
According to a sixth aspect of the invention, in the video projector according to the fifth aspect, wherein the first and second fly-eyed lens, the relay lens, the condenser lenses, the reflection type optical modulation elements, and the projecting lens are disposed so as to satisfy: a relationship (d1/d2)=(f1/f2) where d1 denotes a distance between the first and second fly-eyed lenses, d2 denotes a distance between the relay lens and each of the reflection type optical modulation elements, f1 denotes a focal length of the first fly-eyed lens, and f2 denotes a focal length of the relay lens; and a relationship (1/f3)=(1/d3)+(1/d4) where d3 denotes a distance between the second fly-eyed lens and each of the condenser lenses, d4 denotes a distance between each of the condenser lenses and a pupil position of the projecting lens, and f3 denotes a focal length of each of the condenser lenses.
In the video projectors according to the fifth and sixth aspects of the invention in which the first and second fly-eyed lenses are used as the converting optical system, (1) an image on the outgoing surface of the second fly-eyed lens is converged on the reflection type optical modulation elements without undue loss of light, and (2) an image on the incident surface of the first fly-eyed lens is converted into a small cross-section at the pupil position of the projecting lens. Therefore, all of a light beam emitted from the optical source can be used effectively without undue loss of light. Further, since the number of lenses configuring the lens system disposed between the optical source and the reflection type optical modulation elements can be reduced; the light transmittance can be kept high. As a result, the brightness and the contrast of a projected image on the screen can be increased.
Further, since the diameters of the condenser lenses can greatly be decreased, the video projector can be miniaturized.